In a general semiconductor production process, wafer acceptance test (WAT) is a considerably important in-line test as a basis to judge whether the manufacturing process is acceptable and whether the die is good or bad; also, the test serves as a direct proof of monitoring variations of the manufacturing process.
Besides, compared to the traditional production semiconductor process of electronic integrated circuits, silicon optical waveguides of photonic integrated circuits (photonic ICs) may meet several different problems in manufacturing such as: 1. the layout is more difficult and the design rule checking is more complicated; 2. the structural roughness and etch depth obtained by the manufacturing process is more sensitive; 3. the performance of device process cannot be verified quickly, and the measurement method of optical input and optical output is more complicated than the measurement method of electrical test.
A known measurement method of photonic IC is to fabricate a diffraction grating on a structure of a silicon optical waveguide, and an optical fiber aligns to the diffraction grating to receive diffracted light from the diffraction grating to achieve the purpose of optical output. However, adopting the method is likely to make it uneasy for the optical fiber to align to the diffraction grating with highly precise alignment requirement; thus, it is more difficult for the method to achieve the purpose of optical output. Besides, limited by the size of the diffraction grating and the optical fiber, it is difficult to achieve multiple optical inputs and output ports in a limited area of an photonic IC chip, and an array test is not easy.